Effect of Facet on Local Electron Density of Oxygen Vacancy in Catalysts for Nitrogen Electro-Reduction.

Oxygen-vacancy (Ov) engineering is an effective strategy to manipulate the electronic configuration of catalysts for electrochemical nitrogen reduction reaction (eNRR). The influence of the stable facet on the electronic configuration of Ov is widely studied, however, the effect of the reactive facet on the local electron density of Ov is unveiled. In this work, an eNRR electrode R(111)-TiO2/HGO is provided with a high proportion exposed reactive facet (111) of rutile-TiO2 (denoted as R(111)-TiO2) nanocrystals with Ov anchored in hierarchically porous graphite oxide (HGO) nanofilms. The R(111)-TiO2/HGO exhibits excellent eNRR performance with an NH3 yield rate of 20.68 µg h-1 cm-2, which is ≈20 times the control electrode with the most stable facet (110) exposed (R(110)-TiO2/HGO). The experimental data and theoretical simulations reveal that the crystal facet (111) has a positive effect on regulating the local electron density around the oxygen vacancy and the two adjacent Ti-sites, promoting the π-back-donation, minimizing the eNRR barrier, and transforming the rate determination step to *NNH→*NNHH. This work illuminates the effect of crystal facet on the performance of eNRR, and offers a novel strategy to design efficient eNRR catalysts.